A sugar chain is generally those where a monosaccharide and a monosaccharide are linearly bound via a bond called a glycosyl bond. It is known that various sugar chains have important roles in vivo. Sugar chains often exist in vivo as glycoconjugates bound to a peptide, a protein, a lipid, and the like.
In particular, glycopeptides or glycoproteins that exist in vivo are known to have a sugar chain having a particular structure bound thereto at a particular amino add of the peptide. These sugar chains are known to cause various influences on activity or in vivo kinetics etc. of the peptide (protein), depending on differences in their structure.
These sugar chains or glycosylated peptides are also being used as pharmaceuticals, but it is known that the sugar chain structure will be ununiform when a glycosylated peptide is prepared by a cell line. Since variability in drug effect may be caused when the sugar chain structure is ununiform, there is high necessity for adding separated and purified or chemically synthesized sugar chains with uniform structure to peptides. However, in order to bind separated and purified or chemically synthesized sugar chains to other substances such as peptides, a functional group necessary for binding must be added to the sugar chain as necessary.
As a method for adding a functional group necessary for binding with other substances (also referred to herein as an activating group) to the sugar chain, for example, a method of separating and purifying a sugar chain having an —OH group at the reducing terminal of the sugar chain from a natural egg yolk etc., introducing an amino group at the reducing terminal of the sugar chain by the ammonium carbonate method, and adding an activating group to the said amino group has been performed (see e.g. Patent Literatures 1 and 2 and Non-Patent Literatures 1 and 2). However, with such a method, there was a problem that during the process of introducing an amino group to the sugar chain, the amino group is introduced via ring-opening and ring-dosing of the unit sugar located at the reducing terminal of the sugar chain, and therefore a mixture of α and β anomers is produced even though the configuration of the binding between the sugar chain and the peptide in a naturally-occurring glycopeptide is β-form.